Surface-spintronics device

ABSTRACT

A surface-spintronic device operating on a novel principles of operations may be implemented as a spin conducting, a spin switching or a spin memory device. It includes a magnetic atom thin film ( 13 ) layered on a surface of a solid crystal ( 12 ) and a drain and a source electrodes ( 14 )and ( 15 ) disposed at two locations on the magnetic atom thin film, respectively, whereby a spin splitting surface electronic state band formed in a system comprising said solid crystal( 12 ) surface and said magnetic atom thin film ( 13 ) is utilized to obtain a spin polarized current flow. With electrons spin-polarized in a particular direction injected from the source electrode ( 15 ), controlling the direction of magnetization of the magnetic atom thin film ( 13 ) allows switching on and off the conduction of such injected electrons therethrough. Also, with the use of the magnetization holding function of the magnetic atom thin film ( 13 ), it is possible to realize a spin memory device that can operate to write information on controlling the direction of magnetization of the magnetic atom thin film ( 13 ) and that can operate to read information on detecting the electrodes ( 15, 14 ).

TECHNICAL FIELD

The present invention relates to spintronic (spin electronic) devicesand, more particularly, to a spin conducting, a spin switching and aspin memory device, as a spintronic device.

BACKGROUND ART

Electronics has hitherto placed its basis on a charge of an electron.However, since an electron has a spin as its other attribute besides itscharge and in recent years the limits of electronics placed its basis onthe charge have begun to be seen, researches and developments haverapidly been put forward on spintronics, namely spin electronics, whichis based on the spin of an electron.

For example, as a device utilizing a spin there is now a GMR (GiantMagneto Resistance) device, which has been put to practical use as aread-out device for magnetic hard disk memories, making it possible toachieve their present level storage capacity. There is also as athird-generation spintronic device a MRAM (Magneto Resistive RandomAccess Memory) using TMR (Tunnel Magneto Resistance) effect. The MRAM isbeing put to practical use as a next-generation nonvolatile memory thatis low in power consumption, fast in reading and writing, and highlyintegrated.

In the spintronics, however, there have not yet been realized aconductor for passing a spin current (spin-polarized current) and aswitch for turning on and off a spin current, which are corresponding toan electric current conductor and an electric current switch such as FETrespectively. For example, while it has been proposed to utilizespin-injection from a ferromagnetic metal into a semiconductor, aproblem of losing spin information upon the spin-injection remainsunsolved and the prospect of its utilization can not still be foreseen.

In view of the problem mentioned above, the present invention has forits objects to provide a surface-spintronic spin conducting device thatis capable of flowing a spin current based on a novel principle ofoperation, to provide a surface-spintronic spin switching device that iscapable of switching a spin current with low power consumption, rapidlyand efficiently, and to provide a surface-spintronic spin memory deviceutilizing the same.

DISCLOSURE OF THE INVENTION

In order to achieve an object as mentioned above, there is provided inaccordance with the present invention a surface-spintronic spinconducting device, characterized in that it comprises a solid surface, amagnetic atom thin film layered on the solid surface, and electrodesmounted at two locations on the magnetic atom thin film, wherein aspin-splitting surface electronic state band formed in a systemcomprising the solid crystal surface and the magnetic atom thin film isutilized to cause a spin current to flow. The solid surface ispreferably a nonmagnetic solid surface having surface projected bulkband gaps, which is preferably, e.g., a copper (111) surface or acovalent crystal surface so treated that it is terminated with hydrogen,and the magnetic atom thin film is a magnetic atom thin film having oneto several atomic layers in thickness, e. g., of iron atoms.

According to the makeup mentioned above, a direction of magnetization ofthe magnetic atom thin film determines a spin orientation that cancontribute to conduction in the surface electronic state band, and thesurface-spintronic spin conducting device thus provided causes only aspin current of which the spin is so oriented.

And, if electrons consisting only of up spin or electrons consistingonly of down spin are supplied from the electrode of the spin conductingdevice, a spin current flows when the spin orientation of suppliedelectrons coincides with that of the surface electronic state band andno spin current flows when that is not the case. By controlling thedirection of magnetization in the magnetic atom thin film, it ispossible to make the spin orientation in the surface electronic stateband coincident or not coincident with the spin orientation of thesupplied electrons, and for this reason, it is possible to switch a spincurrent on and off and to realize a spin switching device. The surfaceelectronic state band that can contribute to conduction can be madeeither of up spin only electronic state or down spin only electronicstate, therefore it is possible to switch a spin current on and off atan efficiency of 100%. Also said spin conducting device can be used as aunit element for spintronic logic circuit and as a magneto resistanceelement having an infinite changing rate of resistance. And also, it canalso be used as a spin memory device, because a magnetization directionof the magnetic atom thin film, which is once controlled in onedirection, remains held until next magnetization direction controllingis applied.

The surface-spintronic spin switching device and the surface-spintronicspin memory device in accordance with the present invention includes acontrol means as described below for controlling the direction ofmagnetization in the magnetic atom thin film.

Namely, the surface-spintronic spin switching device and thesurface-spintronic spin memory device may be characterized in that thecontrol means includes a conducting wire disposed laterally adjacent tothe magnetic thin film and a means for flowing an electric currentthrough the conducting wire to generate around it a magnetic field thatis utilized to change the direction of magnetization in the magneticatom thin film normal or reverse.

An alternative form of implementation of the control means in asurface-spintronic spin switching device and a surface-spintronic spinmemory device in accordance with the present invention may becharacterized by including an up spin and a down spin source disposedlaterally adjacent to the magnetic atom thin film; a connection memberconnecting the up spin source to the magnetic atom thin film; aconnection member connecting the down spin source to the magnetic atomthin film; a power supply for injecting spins of the up spin source orspins of the down spin source into the magnetic atom thin film, whereinby applying a voltage of the power supply so as to inject spins of theup spin or down spin into the magnetic atom thin film, its magnetizationdirection is changed into normal or reverse direction. Preferably, theup spin source and down spin source comprise of ferromagnetic metalsmagnetized upwards and downwards respectively, and each of theconnection members comprises of a nonmagnetic metals.

According to the makeup mentioned above, it is possible to magnetize themagnetic thin film controllably in a desired direction and as a resultto switch a spin current on and off. Further, a surface-spintronicdevice according to the present invention, which utilizes a surfaceelectronic state band formed in a system comprising a solid surface anda magnetic atom thin film, can confine a spin current into an extremelysmall space and, as a result, can be made extremely small. Further, inswitching a spin current on and off, the device only requires switchingthe spin orientation in the magnetic atom thin film made of one toseveral atomic layers, normally and reversely. Hence, the requiredenergy is extremely small and there is realized an ultimate energysaving performance.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a graph illustrating a structure of an electronic stateband of copper (111) surface;

FIG. 2 is a graph illustrating computer experimental results for anelectronic state band structure of a system of Cu (111) surface having aFe atomic layer laid thereon;

FIG. 3 shows computer experimental results, represented incrystallographic structural cross-sectional view, for surface structuresof (a) Si (001) surface that has adsorbed Fe atoms and (b) a hydrogenterminated Si (001) surface that has adsorbed Fe atoms;

FIG. 4 is a diagrammatic view in perspective illustrating the makeup ofa surface-spintronic spin conducting device according to the presentinvention;

FIG. 5 is a diagrammatic view in perspective illustrating the makeup ofa surface-spintronic spin switching device according to the presentinvention and having a first magnetization switching means;

FIG. 6 shows diagrams illustrating principles and states ofmagnetization switching in the first magnetization switching means; and

FIG. 7 is a diagrammatic view in perspective illustrating the makeup ofa surface-spintronic spin switching device according to the presentinvention and having a second magnetization switching means.

BEST MODES FOR CARRYING OUT THE INVENTION

The present invention will better be understood from the followingdetailed description and the drawings attached hereto showing certainillustrative forms of implementation of the present invention. In thisconnection, it should be noted that such forms of implementationillustrated in the accompanying drawings hereof are intended in no wayto limit the present invention but to facilitate an explanation andunderstanding thereof.

Hereinafter, the present invention will be described in detail inrespect of suitable forms of implementation thereof with reference tothe drawing figures.

Now, to facilitate understanding of the present invention, anexplanation is given in detail of a surface-spintronic spin conductingdevice. Mention is made preliminarily of spin split surface electronicstate bands formed in a magnetic atom thin film layered on a solidsurface. Although here, for example, the solid surface is shown as acopper (111) surface and a magnetic atom thin film as an iron thin film,it should be understood that this is not a limitation.

Moreover, it is not intended that a surface-spintronic device accordingto the present invention be limited to the makeup described below, andany spintronic device that utilizes a spin split surface electronicstate band should be taken to fall within the present invention.

FIG. 1 (a) is a graph illustrating surface electronic state bands of acopper (111) surface ( see “Physics at Surface” authored by AndrewZangwill (Georgia Institute of Technology), Cambridge University Press,New York New Rochelle Melbourne Sydney). In the graph, the abscissa axisrepresents the wave number towards point M from point Γ in the surfaceplane and the ordinate axis represents the electronic state energy. InFIG. 1( b), the hexagon shown represents the Brillion zone of the copper(111) surface and characters Γ , M and K indicate directions of the wavenumber vector of the graph in a wave number space.

In FIG. 1( a), the shaded area represents a projection of the bandstructure of a copper bulk crystal onto the (111) surface and indicatesthat an electronic state continuously exists in this area of wave numberand energy. If there exists an electron in this shaded area, then theelectron will diffuse into the bulk crystal. Each area unshaved iscalled the surface projected bulk band gap, indicating that an electronhaving a wave number and energy that fall in the area cannot exist inthe bulk crystal. The broken lines represent surface electronic statebands of the copper (111) surface, and especially, the surfaceelectronic state band of the broken line located in the surfaceprojection gap has a surface electronic state which has no intersectionwith any electronic state of the bulk crystal having the correspondingwave number and energy, thus causing an electron having those wavenumber and energy to remain localized having an atomic scale on thesurface. Indeed, such a surface localized state has been confirmed toexist (see “Quantum mirages formed by coherent projection of electronicstructure” authored by H. C. Manichaean, C. P. Lutz & D. M. Eagle,Nature, Vol. 403, pp. 512-515, 2000), and the present invention utilizessuch energy states of electrons which can propagate through a surface.

FIG. 2 is a graph illustrating first principles calculation results ofthe band structure of a system in which one layer of iron atomic thinfilm was laid on a copper (111) surface by the present inventors. Thefirst principles calculation is a computational technique based on thedensity functional theory showing that “the energy of the ground stateof an interacting many-electron system is determined by the densitydistribution of electrons” (see P. Rothenberg and W. Kohn, Phys. Rev.,136, B864 (1964); W. Kohn and L. J. Sham, Phys. Rev., 140, A1133 (1965),see also “Coati Denshi Kozo” (Electronic Structure of Solid State)authored by Takeo Fujiwara, published by Asakura Shoten, Chapter 3). Thefirst principles calculation makes it possible to discuss the electronicstructure of a material quantitatively without an extra empiricalparameter and, indeed, its effectiveness has been proved by a number ofexamples. In this calculation, the generalized gradient approximation isapplied, of which the accuracy is now the highest in the firstprinciples calculation.

In FIG. 2, the curves indicated with marks ♦ represent majority spinelectron band while the curves indicated with marks □ represent minorityspin electron bands. Here, where a system contains electrons each ofwhich has up spin and electrons each of which has down spin, themajority spin means the spin which a larger number of such electronshave and the minority spin means the spin which a smaller number of suchelectrons have. Thus, the spin orientation of the whole, which isdetermined by their total, is equal to the orientation of the majorityspin. And, if a contribution of the orbital magnetic moment is small,then the direction of magnetization is opposite to the spin orientationof the whole, then the direction of magnetization is equal to theorientation of the minority spin. Of electronic state bands as shown,two surface electronic state bands of minority spin S1 and S2 areindicated with solid circles and two surface electronic state bands ofmajority spin S3 and S4 are indicated with broken circles. Here, thesurface electronic state band of minority spin refers to a surfaceelectronic state band having the minority spin localized in an atomicscale on the vicinity of a magnetic atom thin film and orientedperpendicular thereto. Likewise, the surface electronic state band ofmajority spin here refers to a surface electronic state band having themajority spin localized in an atomic scale on the vicinity of a magneticatom thin film and oriented perpendicular thereto

As shown in FIG. 2, a majority spin electronic state and a minority spinelectronic state differ in energy, whereby spin splitting occurs in thissystem. Also a minority spin surface electronic state bands S1, S2 and amajority spin surface electronic bands S3, S4 are formed in differentenergy regions, whereby spin splitting occurs for surface electronicbands. Of them, S1, S2 which exist in a surface projected bulk band gapcan be utilized as an energy state for an electron propagating through asurface. Thus, the minority spin surface electronic state band S1 or S2can be utilized to pass through a surface a spin current consisting onlyof spins of electrons capable of occupying that state.

Note here that which of up spin or down spin is a spin of an electronoccupying the minority spin surface electronic state band S1 or S2 isdetermined by a direction of magnetization in the magnetic atom thinfilm.

An iron atom thin film that is of one or two atomic layers in thicknesshas its easy axis of magnetization perpendicular to its surface andmagnetized upwards or downwards with respect thereto (see “The effect ofspatial confinement on magnetism: films, stripes and dots of Fe on Cu(111)” authored by J. Shen, J. P. Pierce, E. W. Plummer & J. Kirschner,Journal of Physics: Condensed Matter, Vol. 15, R1-R30, 2003).

When the magnetization of an iron atom thin film is oriented upwards(then, the majority spin is the down spin and the minority spin is theup spin; this state is termed to a “normally polarized” state), theminority spin surface electronic bands S1 and S2 can be occupied withelectrons exclusively of up spin. To wit, the electrons which can beinjected into S1 or S2 and are allowed to propagate through the surfaceare electrons exclusively of up spin. On the other hand, when themagnetization of an iron atom thin film is oriented downwards (then, themajority spin is the up spin and the minority spin is the down spin;this state is termed to a “reversely polarized” state), S1 and S2 can beoccupied with electrons exclusively of down spin. To wit, the electronswhich can be injected into S1 or S2 and are allowed to propagate throughthe surface are electrons exclusively of down spin. This can be utilizedto pass either a stream of electrons of up spin or a stream of electronsof down spin selectively and thus to pass a flow of perfect spinpolarized electrons, namely a spin current, through the surface.

Now, in order to form a spin splitting surface electronic state band asmentioned above, it is necessary to form a magnetic atom thin filmwithout destructing the crystallographic structure of a nonmagneticcrystal surface having a surface projected bulk band gap. It has beenreported that depositing an iron atom thin film on a copper (111)surface by the laser MBE method permits forming such an iron atom thinfilm on the copper (111) surface without destructing itscrystallographic structure (see “The effect of spatial confinement onmagnetism: films, stripes and dots of Fe on Cu (111)” authored by J.Shen, J. P. Pierce, E. W. Plummer & J. Kirschner, Journal of Physics:Condensed Matter, Vol. 15,R1-R30, 2003). As another nonmagnetic crystalhaving a surface projected bulk band gap, there is Si (silicon) singlecrystal. With the recognition, however, that iron atoms tend to stripsilicon atoms on a surface of the Si single crystal which is a covalentcrystal, thereby forming suicide, it has hitherto been believed to bedifficult to form an iron atom thin film on such a surface withoutdestructing its crystal structure.

The present inventors have discovered by a computer experiment that ifiron atoms are allowed to deposit on a Si (001) surface that has beenterminated with hydrogen, it is then possible to form an iron atom thinfilm without destroying the Si (001) surface. Results of the computerexperiment are shown below. The method of computation adopted is thefirst principles calculation according to the electronic state computingmethod based on the density functional theory.

FIG. 3 shows computer experimental results, represented incrystallographic structural cross-sectional views, for surfacestructures of (a) a Si (001) surface that has adsorbed Fe atoms and (b)a hydrogen terminated Si (001) surface that has adsorbed Fe atoms. InFIG. 3( a) it is seen that a Fe atom deforms the arrangement of surfaceSi atoms, then combining with a Si atom and that having iron atomsadsorbed to a Si (001) surface as it is destructs the Si surface crystalstructure. On the other hand, it is seen from FIG. 3( b) that the dimmerstructure of surface Si atoms is preserved and that having iron atomsadsorbed on a Si (001) surface that has been ended with hydrogen causesiron atoms to bond with Si without destructing the crystal structure ofthe surface. It follows, therefore, that a Si (001) surface terminatedby hydrogen can be used as a nonmagnetic crystal surface having asurface projection gap for a spintronic device according to the presentinvention.

In particular, noting that the Si (001) surface is the major surface ofa Si wafer for fabricating an integrated circuit in the currentelectronics, the ability to build a spintronic device of the presentinvention on the Si crystal surface is advantageous in that itfacilitates hybridizing conventional electronic circuits with spintroniccircuits.

Referring next to FIG. 4, an explanation is now given in respect of asuitable form of implementation of the surface-spintronic spinconducting device in accordance with the present invention. In FIG. 4,the spin conducting device, designated by reference character 10, isshown comprising a substrate 11, a solid crystal 12, a magnetic atomthin film 13 and a pair of electrodes as a drain and a source electrode14 and 15, respectively. The substrate 11 supports the solid crystal 12formed thereon and is made of an insulating material which should,preferably but not exclusively, be aluminum oxide or the like, when thesolid crystal is copper.

The magnetic atom thin film 13 is formed on a surface of the solidcrystal 12 having a surface projected bulk band gap so that it has afilm thickness of one or several atom layers, and this system has spinsplitting surface electronic state bands (S1, S2) that exist in thesurface projected bulk band gap. Note here that though the magnetic atomthin film 13 is depicted to be rectangular, it may take any desiredpattern to form a given spin current circuit in the spintronics just asa pattern to form an integrated circuit in the conventional electronics.

The drain and source electrodes 14 and 15 are mounted at two locations,respectively, on the magnetic atom thin film. Although the electrodesare each illustratively shown in the form of a probe for a scanningtunneling microscope for contact with the magnetic atom thin film, thecontact may be by way of tunneling contact as in the ordinary use of STMas shown, namely by bringing the probe near the magnetic atom thin filmsurface to bring into point contact therewith, or otherwise by the usualway of sticking each electrode to the surface to establish facialcontact therewith. By applying a bias voltage corresponding in energy toa surface electronic state band between the magnetic atom thin film 13and the source electrode 15, it is possible to inject from the sourceelectrode 15 into the thin film 13 those electrons selectively, whosespin is identical in orientation to the spin of electrons in the surfaceelectronic state band. Electrons so injected are taken out at the drainelectrode 14 which is higher in electric potential than the sourceelectrode 15. In this way, electrons whose spin is identical inorientation to the spin of the surface electronic state band are causedto flow from the source electrode 15 through the magnetic atom thin film13 to the drain electrode 14.

Thus, with the system of a magnetic atom thin film on a solid surface, aperfect spin-polarized electron current, namely spin conducting deviceis made possible, wherein either a flow of electrons of up spin or aflow of electrons of down spin is selectively conducted. In this way,the surface-spintronic spin conducting device 10 can be caused tofunction as a spin conductor. Moreover, since the spin direction of anelectron to be conducted can be determined by the direction ofmagnetization in the magnetic atom thin film, if electrons being fedfrom the source electrode 15 are perfectly spin polarized beforehand byanother surface-spintronic spin conducting device, or the like, it ispossible to switch the conduction of a spin current on and off bymagnetizing the magnetic atom thin film in the normal or the reversedirections.

Referring next to FIG. 5, an explanation is now given in respect of asuitable form of implementation of the surface-spintronic spin switchingdevice in accordance with the present invention. Being asurface-spintronic device, the spin switching element shown designatedby reference character 16 in FIG. 5 incorporates a first mechanism formagnetizing the magnetic atom thin film in the normal and reversedirections, which as a magnetization switching means 20 is added to themakeup of the surface-spintronic spin conducting device 10 describedabove.

The first magnetization switching means comprises two electric currentlines 21 and 22, a power supply 23 for these current lines 21 and 22,and two switches 24 and 25 for passing individual electric currentsthrough the electric current lines 21 and 22 from the power supply 23,respectively.

The current lines 21 and 22, the magnetic atom thin film 13 and thepower supply 23 are arranged and configured so that a magnetic fieldgenerated when the electric current line 21 or 22 has the electriccurrent flow there through has on the magnetic atom thin film acomponent parallel to its easy axis of magnetization and the magneticfield generated by the electric current flow through the electriccurrent line 21 is oriented opposite to that generated by the electriccurrent flow through the electric current line 22. While as shown theelectric current lines 21 and 22 are disposed on the each other sides ofthe magnetic atom thin film 13 and laid parallel to each other to carrythe respective current to flow in the same direction, this is not alimitation. The switch 24 is a switch for normally polarizedmagnetization that can be turned on to cause the current to flow throughthe current line 21 from the power supply 23 while the switch 25 is aswitch for reversely polarized magnetization that can be turned on tocause the current to flow through the current line 22 from the powersupply 23.

In the surface-spintronic spin switching device 16 with the firstmagnetization switching means constructed as mentioned above, theelectric current is passed to flow though the current line 21 from thepower supply 23 when the switch 24 is turned on. This state isillustrated in FIG. 6(A), which depicts a magnetic field distribution ina vertical cross section to the current line 21 and from which it isseen that an upward magnetic field H1 is applied onto the magnetic atomthin film 13 to magnetize it upwards. Thereafter, even with the switch24 turned off, the magnetic atom thin film 13 by its magnetizationholding property remains magnetized upwards, thus retaining the normallypolarized state of magnetization.

Therefore, once the switch 24 is turned on, only electrons of up spincan propagate from the source electrode 15 to the drain electrode 14through the surface electronic state band of the magnetic atom thin film13. The surface-spintronic spin switching device 16 is renderedconductive when only electrons of up spin are supplied from the sourceelectrode 15. The surface-spintronic spin switching device 16 isrendered nonconductive when only electrons of down spin are suppliedfrom the source electrode 15.

Then, if the switch 24 is turned off and the switch 25 is turned on, theelectric current flows through the electric current line 22 from thepower supply 23. This state is illustrated in FIG. 6(B), which depicts amagnetic field distribution in a vertical cross section to the electriccurrent line 22 and from which it is seen that a downward magnetic fieldH2 is applied onto the magnetic atom thin film 13 to magnetize itdownwards. Thereafter, even with the switch 25 turned off, the magneticatom thin film 13 by its magnetization holding property remainsmagnetized downwards, thus retaining the reversely polarized state ofmagnetization.

Therefore, once the switch 25 is turned on, only electrons of down spincan propagate from the source electrode 15 to the drain electrode 14through the surface electronic state band of the magnetic atom thin film13. The surface-spintronic spin switching device 16 is renderednonconductive when only electrons of up spin are supplied from thesource electrode 15. The surface-spintronic spin switching device 16 isrendered conductive when only electrons of down spin are supplied fromthe source electrode 15.

When from this state the switch 24 is again turned on, the magnetizationof the magnetic atom thin film is switched again into the normalpolarity direction so that the surface-spintronic spin switching device16 can conduct only electrons of up spin. Thus, supplied only withelectrons of up spin from the source electrode 15, thesurface-spintronic spin switching device 16 is rendered conductive.Supplied only with electrons of down spin from the source electrode 15,the surface-spintronic spin switching device 16 is renderednonconductive.

In this way, the surface-spintronic spin switching device 16 functionsas a spin switching device which is caused to switch its conductive andnonconductive states for a spin current when the direction of itsmagnetization is switched by the control means.

FIG. 7 shows a surface-spintronic spin switching device 17, whichincorporates a second mechanism as the magnetic polarity switchingmeans. The surface-spintronic spin switching device 17 is constructedhaving the second magnetic polarity switching means added to thesurface-spintronic spin conducting device 10.

The second magnetic polarity switching means comprises two spin sources31 and 32 which are magnetized parallel to an easy axis of magnetizationof the magnetic atom thin film 13 and mutually opposite direction; twoconnections 31 a and 32 a that connect the magnetic atom thin film 13 tothe two spin sources 31 and 32, respectively; a power supply 33 forproviding a bias voltage for spin injection; and two switches 34 and 35for it. The spin sources 31 and 32 are made of ferromagnetic metalswhich are magnetized in the same directions which are identical to thedirections of magnetization in which the magnetic atom thin film 13 areto be normally and reversely magnetized, respectively. Advantageouslybut not exclusively, the spin sources 31 and 32 are the ferromagneticmetals magnetized upwards and downwards directed perpendicular to theirsurfaces, respectively, when the solid surface 12 is a copper (111)surface and the magnetic atom thin layer 13 is an iron thin film.

Further, for spin injection by applying a bias voltage between the spinsource 31 or 32 and the magnetic atom thin layer 13, the spin sources 31and 32 are connected to the magnetic atom thin film via the connectionmembers 31 a and 32 a, respectively. The connection members 31 a and 32a may be sufficient if they permit spin injection from the spin sources31 and 32 into the magnetic atom thin film 13 but are preferably made ofnonmagnetic and electrically conductive material whose lattice constantis close to those of the atomic thin film 13 and the spin sources 31 and32.

The switch 34 is a switch for normally polarized magnetization that canbe turned on to apply a bias voltage of a selected magnitude from thepower supply 33 between the spin source 31 and the magnetic atom thinfilm 13. And, the switch 35 is a switch for reversely polarizedmagnetization that can be turned on to apply a bias voltage of aselected magnitude between the spin source 32 and the magnetic atom thinfilm 13.

In the surface-spintronic spin switching device 17 with the secondmagnetic polarity switching means constructed as mentioned above,turning the switch 34 on causes the bias voltage to be applied betweenthe spin source 31 and the magnetic atom thin film 13 and normallypolarized spins to be injected into the magnetic atom thin film 13 fromthe spin source 31, thereby magnetizing the magnetic atom thin film 13in the normal direction. Thereafter, even with the switch 34 turned off,the magnetic atom thin film 13 by its magnetization holding propertyremains in the state of magnetization in the normal direction.

Therefore, once the switch 34 is turned on, only electrons of up spincan propagate from the source electrode 15 to the drain electrode 14through the surface electronic state band of the magnetic atom thin film13. The surface-spintronic spin switching device 17 is renderedconductive when only electrons of up spin are supplied from the sourceelectrode 15. The surface-spintronic spin switching device 17 isrendered nonconductive when only electrons of down spin are suppliedfrom the source electrode 15.

After the switch 34 is turned off, if the switch 35 is turned on, thebias voltage is applied between the spin source 32 and the magnetic atomthin film 13 to inject reversely polarized spin into the magnetic atomthin film 13 from the spin source 32. This causes the magntic atom thinfilm 13 to be magnetized in the reverse direction. Thereafter, even withthe switch 35 turned off, the magnetic atom thin film 13 by itsmagnetization holding property remains in the state of magnetization inthe reverse directon.

Therefore, once the switch 35 is turned on, only electrons of down spincan flow from the source electrode 15 to the drain electrode 14 throughthe surface electronic state band on the magnetic atom thin film 13. Thesurface-spintronic spin switching device 17 is rendered conductive whenonly electrons of down spin are supplied from the source electrode 15.The surface-spintronic spin switching device 17 is renderednonconductive when only electrons of up spin are supplied from thesource electrode 15.

After the switch 35 is turned off, if the switch 34 is again turned on,the magnerization of the magnetic atom thin film 13 is switched againinto the normal polarity direction so that the surface-spintronic spinswitching device 17 can conduct only electrons of up spin. Thus,supplied only with electrons of up spin from the source electrode 15,the surface-spintronic spin switching device 17 is rendered conductive.Supplied only with electrons of down spin from the source electrode 15,the surface-spintronic spin switching device 17 is renderednonconductive.

In this way, the surface-spintronic spin switching device 17 functionsas a spin switching device which is caused to switch its conductive andnonconductive states for a spin current when the polarity of itsmagnetization is switched by normally and reversely polarizing spininjections effected by the second control means.

While each of the surface-spintronic spin switching device 16 and 17 hasbeen shown and described as functioning as a spin switching device thatis controllably rendered conductive and nonconductive for a spin currentpropagating through the magnetic atom thin film, this is not theirexclusive use but they can also be used as a surface-spintronic spinmemory device using the fact that once the element is switched to anormally or reversely magnetized state, it can retain that state in themagnetic atom thin film until it is switched to the reversely ornormally magnetized polarity state. To wit, it is possible to use adirection of magnetization as storage information, to use themagnetization switching means to perform the operation of writing theinformation, and to detect the state of conduction or nonconductorbetween the source and drain electrodes 15 and 14 for a spin current toperform the operation of reading the information.

Although the present invention has hereinbefore been set forth withrespect to certain illustrative embodiments thereof, it will readily beappreciated to be obvious to those skilled in the art that manyalterations thereof, omissions there from and additions thereto can bemade without departing from the essences of scope of the presentinvention. Accordingly, it should be understood that the invention isnot intended to be limited to the specific embodiments thereof set forthabove, but to include all possible embodiments that can be made withinthe scope with respect to the features specifically set forth in theappended claims and to encompass all the equivalents thereof.

Industrial Applicability

To establish a state of electrons that bear conduction, asurface-spintronic device according to the present invention utilizes aspin splitting surface electronic state band formed in a systemcomprised of a solid surface and a magnetic atom thin film layeredthereon. Thus, a spin conducting device is realized that can carry aperfect or nearly perfect spin polarized electric current, namely a spincurrent. Since it allows defining the spin direction of electrons topropagate by controlling the direction of magnetization in the magneticatom thin film, there is also realized a spin switching device forswitching a spin current between states of conduction and nonconductor.Further, using the fact that the magnetic atom thin film externallycontrolled and thereby brought into a state of magnetization holds thatstate until a next control is effected thereon, there is realized a spinmemory device that can operate to write information on controlling thedirection of magnetization of the magnetic atom thin film and to readinformation on detecting the state of conduction or nonconductor for aspin current. Also, constructed by a system of a solid surface and amagnetic atom thin film layered thereon, the device can confine a spincurrent into an extremely small space and, as a result, can be madeextremely small. Further, in switching a spin current on and off, thedevice only requires switching the spin polarization normally andreversely in a magnetic atom thin film made of one to several atomiclayers. Hence, the required energy is extremely small and there isrealized an ultimate energy saving performance. Further, since theswitching or memory writing is confined into the micro fine area and isperformed by magnetizing normally and reversely the magnetic atom thinfilm of one to several atomic layer thickness, an ultimate energy savingperformance is also achieved. Consequently, there is provided inaccordance with the present invention a device that can be implementedas a spin conducting, a spin switching and a spin memory device in thespintronics and also as a magneto resistance device that is extremelylarge in resistance change.

1. A surface-spintronic spin conducting device, characterized in that itcomprises a solid surface, a magnetic atom thin film layered on asurface of a solid crystal, and electrodes mounted at two locations onsaid magnetic atom thin film, whereby a spin splitting surfaceelectronic state band formed in a system comprising said solid crystalsurface and said magnetic atom thin film is utilized to cause a spincurrent to flow.
 2. A surface-spintronic spin conducting device as setforth in claim 1, characterized in that said solid surface is anonmagnetic solid surface having a surface projected bulk band gaps andsaid magnetic atom thin layer is a magnetic atom thin film having athickness of one to several atom layers.
 3. A surface-spintronic spinconducting device as set forth in claim 2, characterized in that saidnonmagnetic crystal surface is a copper (111) surface and said magneticatom thin film is an iron atom thin film.
 4. A surface-spintronic spinconducting device as set forth in claim 2, characterized in that saidnonmagnetic crystal surface is a covalent crystal surface so treatedthat it is terminated with hydrogen and said magnetic atom thin film isan iron atom thin film.
 5. A surface-spintronic spin switching device,characterized in that it comprises a solid crystal surface, a magneticatom thin film layered on a surface of the solid crystal, electrodesdisposed at two locations on said magnetic atom thin film, and a controlmeans for controlling the direction of magnetization in said magneticatom thin film, whereby controlling, by said control means, the spinstate of a spin splitting surface electronic state band formed in asystem comprising said solid crystal surface and said magnetic atom thinfilm causes switching on and off a spin current of either a flow ofelectrons of up spin or a flow of electrons of down spin, of electronssupplied through one of said electrodes from an external spin conductingdevice.
 6. A surface-spintronic spin switching device as set forth inclaim 5, characterized in that said solid surface is a surface of anonmagnetic crystal having a surface projected bulk band gaps and saidmagnetic atom thin film is a magnetic atom thin film having a thicknessof one to several atom layers.
 7. A surface-spintronic spin switchingdevice as set forth in claim 6, characterized in that said nonmagneticcrystal surface is a copper (111) surface and said magnetic atom thinfilm is an iron atom thin film.
 8. A surface-spintronic spin switchingdevice as set forth in claim 6, characterized in that said nonmagneticcrystal surface is a covalent crystal surface so treated that it isterminated with hydrogen and said magnetic atom thin film is an ironatom thin film.
 9. A surface-spintronic spin switching device as setforth in claim 5, characterized in that it has a control means includinga conducting wire disposed laterally adjacent to said magnetic atom thinfilm and a means for passing an electric current through said conductorto generate around it a magnetic field that is utilized to change thedirection of magnetization in said magnetic atom thin film.
 10. Asurface-spintronic spin switching device as set forth in claim 5,characterized in that said means for controlling the direction ofmagnetization in said magnetic atom thin film includes: an up spin and adown spin sources disposed laterally adjacent to said magnetic atom thinfilm; a connection member connecting said up spin source to saidmagnetic atom thin film; a connection member connecting said down spinsource to said magnetic atom thin film; a power supply for injectingspins of said up spin source and spins of said down spin source intosaid magnetic atom thin film, and further a means for applying a voltagefrom said power supply so as to inject spins of said up spin or downspin sources into said magnetic atom thin film, thereby switching itsmagnetization into a normal or reverse polarity direction.
 11. Asurface-spintronic spin switching device as set forth in claim 10,characterized in that said up spin and down spin sources compriseferromagnetic metals magnetized downwards and upwards, respectively, andeach of said connection members comprises a nonmagnetic metal.
 12. Asurface-spintronic spin memory device, characterized in that itcomprises a solid surface, a magnetic atom thin film layered on asurface of the solid crystal, electrodes disposed at two locations onsaid magnetic atom thin film, and a control means for controlling thedirection of magnetization in said magnetic atom thin film, wherebycontrolling, by said control means, the spin state of a spin splittingsurface electronic state band formed in a system comprising said solidsurface and said magnetic atom thin film causes switching on and off aspin current of either a flow of electrons of up spin or a flow ofelectrons of down spin, of electrons supplied through one of saidelectrodes from an external spin conducting device, and wherein saidmagnetic atom thin film has a magnetization holding property that isutilized to store information.
 13. A surface-spintronic spin memorydevice as set forth in claim 12, characterized in that said solidcrystal surface is a surface of a nonmagnetic crystal having a surfaceprojected bulk band gaps, and said magnetic atom thin film is a magneticatom thin film having a thickness of one to several atom layers.
 14. Asurface-spintronic spin memory device as set forth in claim 13,characterized in that said nonmagnetic crystal surface is a copper (111)surface and said magnetic atom thin film is an iron atom thin film. 15.A surface-spintronic spin memory device as set forth in claim 13,characterized in that said nonmagnetic crystal surface is a covalentcrystal surface so treated that it is terminated with hydrogen and saidmagnetic atom thin film is an iron atom thin film.
 16. Asurface-spintronic spin memory device as set forth in claim 12,characterized in that it has a control means including a conducting wiredisposed laterally adjacent to said magnetic thin film and a means forpassing an electric current through said conductor to generate around ita magnetic field that is utilized to change the direction ofmagnetization in said magnetic atom thin film.
 17. A surface-spintronicspin memory device as set forth in claim 12, characterized in that saidcontrol means for controlling the direction of magnetization in saidmagnetic atom thin film includes: an up spin and a down spin sourcesdisposed laterally adjacent to said magnetic atom thin film; aconnection member connecting said up spin source to said magnetic atomthin film; a connection member connecting said down spin source to saidmagnetic atom thin film; a power supply for injecting spins of said upspin source and spins of said down spin source into said magnetic atomthin film, and further a means for applying a voltage from said powersupply so as to inject spins of said up spin or down spin source intosaid magnetic atom thin film, thereby switching its magnetization into anormal or reverse polarity direction.
 18. A surface-spintronic spinmemory device as set forth in claim 17, characterized in that said upspin and down spin sources comprise ferromagnetic metals magnetizeddownwards and upwards, respectively, and each of said connection memberscomprises a nonmagnetic metal.